In the punch and die art and particularly in the field of high-speed automated forming and punching equipment for punching and forming sheet material, e.g., sheet metal and especially in the case of automated turret punch presses, the punch presses are operated by computer to rapidly perform a series of punching or forming operations. These punch presses which by themselves form no part of the present invention are typically provided with an upper turret and a lower turret that rotate and are indexed intermittently between punching operations. The turrets may, for example, hold as many as a dozen or more separate punches such as hole punches that are used one after another for performing given operations. When a punch is struck from above by the ram of the punch press, the punch element or punch insert is driven downwardly through the workpiece to perform the punching or forming operation. When released, the punch insert is retracted by a spring provided in the punch assembly.
While there have been several attempts to provide a satisfactory marking tool for punch presses, the prior tools are provided with characters that must be changed manually or in other equipment are able to make an impression of only one letter or number at a time. U.S. Pat. No. 5,993,090, for example, describes a marking punch provided with twelve letters, each of which is punched separately. So, for example, to punch the number 2007 would require four punch strokes and some mechanism for rotating the punch shaft between strokes but none is provided. U.S. Pat. No. 4,397,233 describes an automatic numbering assembly that instead of making an impression into the workpiece, transfers ink from an ink roller to a package as the drum rotates. Thus, the patented device is not suitable for making an impression in metal nor for being operated by the reciprocating ram of a punch press. A multicharacter punch numbering stamp has been made for a punch press by the Conic Company Ltd. of Okayama, Japan, but the digits of the numbering wheel must be individually set by hand between stamping operations. Thus each time the machine is run, it will continue to stamp the same number until the press is stopped and the wheels are rotated by hand to provide a new number. While numbering devices themselves are available commercially, there is no way to operate them using a high speed computer controlled punch press. Consequently, as far as the applicants were able to determine, no punch press tool for stamping successive multicharacter impressions into a workpiece has been developed that is able to be actuated by the rapidly reciprocating ram of an automated punch press and is capable of successively stamping numbers or other characters in sequence into a workpiece such as a sheet of metal.
In view of these and other deficiencies of the prior art, it is one object of the present invention to find a way to enable a high speed computer operated punch press to reliably impress alphanumeric characters or other indicia a selected depth into the surface of a workpiece and to advance the characters each cycle of the press ram.
Another object of the invention is to provide a device of the kind described in which the characters to be stamped are extended out below the unit but not far enough to strike objects unintentionally as the punch press operates and are preferably able to accommodate workpieces of various thicknesses.
These and other more detailed and specific objects and advantages of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.